The present invention relates to a magnetoresistance effect film, a magnetoresistance effect head using said film, and a solid state memory using said film.
Recording density of hard disks have been increased 100% every year. To continuously increase the recording density, resolution of a reproducing head, which is assembled in a hard disk drive unit, in a direction of gap-length, must be improved, and a width of a magnetoresistance effect element of the reproducing head in a direction of track width must be narrower. Thus, in a conventional reproducing head, the resolution is improved by making the gap-length short, and the width of the element is made narrower.
Magnetoresistance effect films are shown in FIGS. 10 and 11. Two types of magnetoresistance effect elements are used for reproducing heads of hard disk drive units. One is a CIP (Current In-Plane) type, in which a sensing current passes in a plane of a magnetoresistance effect film (see FIG. 10); the other is a CPP (Current Perpendicular to Plane) type, in which a sensing current passes perpendicular to a plane of a magnetoresistance effect film (see FIG. 11).
In the magnetoresistance effect head shown in FIG. 10, the magnetoresistance effect film 10 is sandwiched between a lower insulating layer 12 and an upper insulating layer 14, further they are sandwiched between a lower shielding layer 16 and an upper shielding layer 18. The magnetoresistance effect head has biasing layers 22 and terminal layers 24.
On the other hand, in the magnetoresistance effect head shown in FIG. 11, the magnetoresistance effect film 10 is sandwiched between the lower shielding layer 16 and the upper shielding layer 18. The magnetoresistance effect head has insulating layers 20 and the biasing layers 22.
The gap-length relating to the resolution of reproducing signals is defined as a distance of the narrowest gap between the lower shielding layer and the upper shielding layer, which sandwich the magnetoresistance effect element. In the CIP type head, the gap is the sum of thickness of the lower shielding layer, the magnetoresistance effect film and the upper shielding layer; in the CPP type head, the gap is thickness of the magnetoresistance effect film including the terminal layers. The narrower the gap-length is made, the more the resolution of the reproducing head is improved. Therefore, the thickness of the magnetoresistance effect film has been made thinner so as to improve the resolution of the reproducing head.
Effectively reducing the width of the magnetoresistance effect element with reducing the thickness of the magnetoresistance effect film will be explained.
A method of manufacturing the CIP type head is shown in FIGS. 12A–12F. Note that, the CPP type head is manufactured by similar method. Firstly, the lower shielding layer 16 and the lower insulating layer 12 are formed, then a magnetoresistance effect film 30 is formed on the lower insulating layer 12 by sputtering (see FIG. 12A). Next, a resist pattern 32, which defines the width of the magnetoresistance effect element, is formed by photolithography (see FIG. 12B). The width of the resist pattern 32 is, for example, 0.05–0.2 μm.
Successively, the magnetoresistance effect film 30 is etched by ion beams (see FIG. 12C). At that time, the resist pattern 32 acts as a mask. Parts of the magnetoresistance effect film 30 which are not covered with the resist pattern 32 are sputter-etched by ion beams, a part of sputtered atoms stick on side walls of the resist pattern 32. For example, in the case of the magnetoresistance effect film 30 having effect thickness of 38 nm, thickness of the stuck atoms is 16–28 nm. The more the magnetoresistance effect film 30 is etched, the thicker the thickness of the stuck atoms becomes. Therefore, if the thickness of the magnetoresistance effect film 30 is thin, the thickness of the stuck atoms can be thin.
After the etching step, a hard film, which controls magnetic zones of the magnetoresistance effect film 30, and a sputtered film 34, which will be terminals for supplying an electric current, are formed (see FIG. 12D), then disused parts are removed together with the resist (see FIG. 12E). Finally, the upper insulating layer 14 and the upper shielding layer 18 are formed (see FIG. 12F).
In the step shown in FIG. 12D, if the thickness of the sputtered film 34 is too thick, distances from the hard film and the terminals to the magnetoresistance effect element are long, so that the total width of the element must be greater. For example, in the case of the magnetoresistance effect film 30 having the effect thickness of 38 nm, the thickness of the stuck atoms on one side is 16–28 nm. Therefore, the width of the element must be added 0.032–0.056 nm. Since width of conventional elements are 0.1–0.2, the additional width is great. To effectively prevent forming the wider element, the total thickness of the magnetoresistance effect film 30 should be thinner.
A method of manufacturing a CIP type head with a thin magnetoresistance effect film, whose thickness is thinner than that of the magnetoresistance effect film used in the method shown in FIGS. 12A–12F, is shown in FIGS. 13A–13F.
If the total thickness of the magnetoresistance effect film is thin, the thickness of the stuck layer formed in the etching step shown in FIG. 13C is mostly in proportion to the total thickness of the magnetoresistance effect film 10. For example, in the case of magnetoresistance effect film 10 whose thickness is reduced from 34.6 nm to 19.6 nm, the thickness of the stuck layer can be reduced from 16–28 nm to 9–16 nm. Therefore, width of a core shown in FIG. 13E can be reduced 38 nm or less. Width of the resist pattern is 50–200 nm, so the reducible width is an important factor for reducing the width of the core. Further, if the magnetoresistance effect film is made thinner, the gap-length is also made shorter. For example, if the thickness of the insulating layers 12 and 14 are 18 nm, the gap-length of the reproducing head shown in FIG. 12F is 70.6 nm; on the other hand, the gap-length of the reproducing head shown in FIG. 13F is 55.6 nm. Namely, the gap-length can be shorter 22% with the thin magnetoresistance effect film.
As described above, the thin magnetoresistance effect film is capable of reducing the width of the core and the gap-length. Conventionally, an antiferromagnetic film about 10–15 nm thick is used to fix a magnetizing direction of a pinned magnetic layer in the magnetoresistance effect film, so it is difficult to make the total thickness of the magnetoresistance effect film 30 nm or less. A constitution of an ordinary magnetoresistance effect film of the CIP head is, for example, NiCr 5.0 nm/PtMn 13.0 nm/CoFe 1.5 nm/Ru 0.8 nm/CoFe 2.3 nm/Cu 2.0 nm/CoFe 1.0 nm/NiFe 3.0 nm/Ru 1.0 nm/Ta 5.0 nm. Therefore, the total thickness is 34.6 nm. On the other hand, a constitution of an ordinary magnetoresistance effect film of the CPP head is, for example, NiCr 5.0 nm/PtMn 13.0 nm/CoFe 1.5 nm/Ru 0.8 nm/CoFe 2.3 nm/Cu 2.0 nm/CoFe 1.0 nm/NiFe 2.0 nm/CoFe 1.0 nm/Cu 2.0 nm/CoFe 2.3 nm/Ru 0.8 nm/CoFe 2.0 nm/PtMn 13.0 nm/Ta 5.0 nm. Therefore, the total thickness is 53.7 nm.
In the CIP head, 38% (48% in the CPP head) of the total thickness of the magnetoresistance effect film is PtMn. To have enough antiferromagnetic property, the thickness of PtMn must be 13 nm or more. Therefore, it is difficult to make the thin magnetoresistance effect film including PtMn. Namely, the thickness of the antiferromagnetic layer(s) is about 50% of the total thickness of the conventional magnetoresistance effect film, and it cannot be thinner than a prescribed thickness to have enough function, so that reducing the thickness of the magnetoresistance effect film is limited.